Stabilized acrylonitrile polymers



Patented Nov. 11, 1952 4 UNITED STATES PATENT OFFICE STABILIZED .ACB LOITBILE OLYMERS Robert J. Slocombe, Dayton, and George L, Wesp,

vEng uw d, Ohi ass s s. o Mo s C mical Qompany, St. Louis, Mo., acorporation of Delaware No Drawing.

This inv tion relates to methods or r p ins pol mers of aer lonltr lewhic are tab e wi hrespect to thermod soo orat on- More specifically'theinvention relates to methods of converting unstable polymersofacrylonitrile into color stable polymers,

Alt hough polyacrylonitrile and copolymers of 5c e v cent or more by weiht of acrylonitrile and other monomers containin olefin o un atuationcopolymerized therewith, are neral r ard d as being materials o g odthermostahil ty, hey a e su ject to discol ration- This phenomenongenerally results because of the need forextruding and molding thecomposi tion at elevated temperatures. Furthermore, the higheracrylonitrile polymers find extensive use in the fabrication of fibers,films and fabrics whi h frequen y are su jected to iron ng p ati ns ateleva d te peratu es- Thus, s rious disoolorations are oft ndevelooedinthe fabricaion a d process ng o .a rylon' .e po mers The prim ry purp seof this inven on is to provide color stable polymers of acrylonitrile. Afurther purpose ofthe invention is to facilitate molding and otherprocessing procedures withoutthe danger of the deterioration of fibersand other forms usually encountered at elevated temoeratures. A still futher purp se o the inve tion is to provide substances which can be addedto conventional polymers to induce resistance to heat and discolo ation-It has been discovered that by addin acids of boron and es ers ther ofto acryl nitrile polymers improved resistance to discoloration mayreadily be developed. The nature of the chemical reaction involved isnot definitely understood, but it is believed that the color change isdue to some impurities present in the polymer. It may be that the boroncontaining radicals react with the impurity to form a substance which ismore heat stable than the impurity in its original form. Since not allboron compounds produce the same degree of beneficial effect thephenomena apparently involve additional stabilization by the metal aswell as the acid portion of the compound. The total stabilization mayinvolve addi- Application October 26, 1950, Serial No. 192,345

'12 Claims. (Cl. 260-457) of a wide variety of other unsaturatedsubstances known to be copolymerizable with the acrylonitrile. Thus, theinvention is practicable with the well-known fiber forming copolymers ofacrylonitrile, which may be the copolymers of 75 per cent or more percent of acrylonitrile and up to 25 per cent of other monomers. Othercopolymers of from 25 per cent to 75 percent acrylonitrile and 75 to 25per cent of the various other monomers, which copolymers have primaryutility in the held of film and molding composition mouction, are alsouse ul- The said other monomers with which the acrylonitrile may be o omer ed to produce resinous su stan capable of use in the p a tic of thisin n n incl de inyl acet e a d o her n l ters oi m ca oxyl c acidshaving p to f ur carbon at ms i t e carb xylic acid ra il, dimethyl maeat and d methy iumarat and. other alk l. esters of meri a me ids,wherein the allryl radical has up to fou arbon at m methyl methacrylateor ,aorylate and other alkyl acrylates and alkyl met aorylates whereinthe alkyl radical vhas up to four carbon toms, vin l chl d and thervinyl halid s styrene, alpha -methylstryrene and other vinyl andisopropenyl substituted aromatic hydrocarbons, methacrylonitrile,vinylidene chloride, vinylpyridine, the vinyl derivatives of other alkyl su s tu ed pyr dines. and the vin l d rivatives of other compoundscon aining a tertiary amino atom in a heterocyclic ring,vinylchloroacetate and other vinyl esters of haloacetic acids,methallyl, chloroacetate, allyl chloroacetate and chloroa ylohloro oetee. and. the corresponding ester of other 7 haloacetic esters,vinylimidazole and other N-vinyl derivatives or heterocy lic nitr encompounds, and one or more of these and other unsaturated compoundsknown to be copolymerizable with acrylonitrile.

The boron compounds which are useful in the practice of this inventionare the acids of boron and the esters of the various boric acids, forexample, orthoboric acid, borio anhydride, metaboric acid, tributylborate, and triethyl borate. A wide variety of other boron compounds maysimilarly be used. In the practice of this invention the stabilizer maybe used to the extent of 0.01 per cent to ten per cent by weight of theacrylonitrile polymer to be stabilized. Preferred practics of thisinvention involves the use of 0.1 per cent to three per cent of thestabilizer.

The invention may be practiced by combining the acrylonitrile polymerand the boron compound by a wide variety of mechanical procedures. Thus,the polymer may be treated in granular solid form and mixed physicallywith the compound or an aqueous or other liquid solution or dispersionof the compound. The physical mixture may take place at room temperatureor at higher temperatures, for example the temperature at which thepolymer is semisolid or fluid. A preferred practice involves the use ofsolvents or plasticizers for the acrylonitrile polymers in the presenceof which the intimate dispersing of the stabilizing additive and theacrylonitrile polymer is more readily efiected. The nature of thesolvent which is useful in dissolving or softening the acrylonitrilepolymer will to a large extent depend upon the chemical composition ofthe acrylonitrile polymers.

The copolymers of 75 per cent or more of various compounds in the tablebelow. Films were prepared therefrom and tested to determine the lighttransmission properties by photoelectrio methods. The transmissionvalues set forth in the table below were measured after forty minutesand three hour periods of exposure at acrylonitrile and up to per centof the comonomer are well-known fiber forming compositions andaregenerally resistant to the effect of most chemical solvents. In thepreparation of solution of such copolymers, solvents, such asN,N-dimethylformamide, N,N-dimethylacetamide, gamma-butyrolactone,ethylene carbonate, maleic acid, alpha-cyanoacetamide, andtris(dimethylamido)phosphate may be used.

, In the treatment of the more soluble types of acrylonitrile polymers,for example those of from 20 per cent to '75 per cent acrylonitrile andfrom 25 per cent to 80 per cent of other monomers copolymerizabletherewith, the selection of a solvent is less critical. This type ofcopolymer may be dissolved or otherwise physically effected by thevarious ketones, esters and aromatic hydrocarbon types of solvents. Ingeneral, the copolymer is placed in a suitable solution, or softened andswelled by the selected medium so as to enable a more ready dispersionof the boron compound within the solid polymer. Obviously a solventwhich is also capable of dissolving at least to some extent the boroncompound to be used will be exceptionally beneficial. However, theselection of the dispersing agent, the stabilizing agent and theparticular method of dispersing the compound in the solid polymer 1 is amatter readily determined by one skilled in the art. Y

To evaluate the stabilizing action of various compounds, acrylonitrilepolymers of different chemical and physical properties were used and thecompound dispersed therein by a variety of methods.

Example Polyacrylonitrile was stabilized by dissolving it inN,N-dimethylformamide and adding to separate solutions two per cent ofeach of the a temperature of 180 C. The ratings are expressed in thepercentage of the transmission in excess of the transmission through asample of the identical polymer not containing the stabilizing agentusing a 410 millimicron filter in the photometer.

Orthoboric acid +30.7 +473 Meta-boric acid +383 +375 Boric anhydride+272 +44.9 Tributyl borate +29.7 +215 What we claim is: 1. A stablepolyacrylonitrile polymer comprising a polymer of 20 per cent to 100 percent of acrylonitrile and up to per cent of another olefinic monomercopolymerizable therewith, said polymer' containing intimately dispersedtherein from 0.01 to ten per cent of a compound of the group consistingof the acids of boron and esters thereof.

2. A stable polyacrylonitrile polymer comprising a polymer of 20 percent to per cent of acrylonitrile and up to 80 per cent of anotherolefinic monomer copolymerizable therewith, said polymer containingintimately dispersed therein from 0.1 to three per cent of a compound ofthe group consisting of the acids of boron and esters thereof.

3. The stable polymer of claim 1 wherein the dispersed compound isorthoboric acid.

4. The stable polymer of claim 1 wherein the dispersed compound ismeta-boric acid.

5. The stable polymer of claim 1 wherein the dispersed compound is boricanhydride.

6. The stable polymer of claim 1 wherein the A dispersed compound istributyl borate.

No references cited.

1. A STABLE POLYACRYLONITRILE POLYMER COMPRISING A POLYMER OF 20 PERCENT TO 100 PER CENT OF ACRYLONITRILE AND UP TO 80 PER CNET OF ANOTHEROLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, SAID POLYMER CONTAININGINITMATELY DISPERSED THEREIN FROM 0.01 TO TEN PER CNET OF A COMPOUND OFTHE GROUP CONSISTING OF THE ACIDS OF BORON AND ESTERS THEREOF.